Recent developments in electric satellite propulsion make it possible to envisage performing a large part of the transfer by using this electric propulsion. Since this propulsion has a much better efficiency, it is then possible to lower the mass upon the launching of the satellites for equal missions.
The main drawback with electric propulsion is its weak thrust, which substantially increases the time needed for the transfer. In order to control this time, it is then necessary to increase the thrust to the maximum of the capabilities of the satellite.
Another feature of electric thrusters is the fact that the thruster is optimized for its maximum operating point. When the thruster is used with a lesser power, its efficiency (mN/W) and its specific impulse decrease.
Since the cost of the electric propulsion systems is high, the most common configuration is to have four thrusters mounted on pointing mechanisms. These thruster/mechanism assemblies are formed preferably toward the anti-earth face of the satellite.
To perform an electric transfer maneuver with maximum thrust, all four thrusters are used in parallel.
In the event of failure of one of the four active thrusters, the known solutions for mitigating the lack of a thruster are:
either to use two thrusters. Now, the drawback is that, in this case, the transfer time increases. In the worst case in which the failure occurs at the beginning of the LEOP (Launch an Early Orbit Phase—phase beginning upon the separation from the launch vehicle and ending when the satellite is operational in its final orbit) with a power dimensioning in which the four thrusters are used at 100%, the transfer time can be doubled;
or to use the mechanisms on which thrusters are mounted in order to repoint the three remaining thrusters toward the center of gravity. Now, the drawback is that the xenon consumption increases and the transfer time is not optimized.
Thus, there is a need for a solution which mitigates the various drawbacks in the prior art solutions to perform an electric transfer with a maximum thrust in the event of failure of one thruster out of the active thrusters of a satellite. The present invention meets this need.